* Soybeans at highest since June 2016, up 12% this month * Strong demand and dry South American weather support * Corn hits highest since July 2019, wheat ends mixed (Adds wheat turning mixed, adds closing prices) CHICAGO, Nov 20 (Reuters) - U.S. soybean futures rose for a sixth consecutive session on Friday and hit a four-year high on dry conditions in key South American crop areas and concerns about dwindling U.S. supplies. Corn also gained on strong exports and worries about South American dryness, while wheat ended mixed. All three markets finished below their session highs as end-of-week profit-taking clipped gains. Still, corn and soybeans posted solid weekly gains for a third straight week on worries that demand must slow further to ration tightening supplies. “There is a scarcity concern in the market this year,” said Rabobank commodity analyst Michael Magdovitz. “We’re getting into the period when there is a higher moisture requirement for the Brazilian crop and when there is not so much U.S. crop left to be sold.” While some rain has reached Brazilian and Argentine grain belts, more moisture was seen as needed to complete soybean and corn planting and boost crop development. Argentine soy planting advanced sharply over the past week after rains in key drought-hit areas, the Buenos Aires Grains Exchange said on Thursday, though much of the country remained dry. “The South American forecast still looks dry for most of Argentina, and warmer than expected. It’s a very concerning weather forecast,” said Brian Hoops, president of U.S. broker Midwest Market Solutions. Chicago Board of Trade (CBOT) January soybean futures was 3-1/2 cents higher at $11.81 per bushel after peaking earlier at $11.96-3/4, its contract high and the highest for a most-active contract since June 13, 2016. December corn futures ended 3/4 cent higher at $4.23-1/4 a bushel. March futures were a penny higher at $4.28-1/4 after peaking at $4.33-1/4, the loftiest level for a most active contract since July 24, 2019. CBOT December wheat closed 1-1/2 cents higher at $5.93-1/4 per bushel.